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Bring in fresh air? How will that solve the humidity problem unless you can bring the air in form Arizona. I agree with fresh air to purge pollutants and replace oxygen.
What size should the a/c be to keep the home dry with 70^F outdoors with rain for a week? It must be Zero tons but run all the time, right!
Seriously, you're decreasing air infiltration and heat gain from outdoors which is good. For real indoor air quality, consider fresh air ventilation and real humidity control from a whole house ventilating dehumidifier. This provides absolute humidity control totally independent of the a/c load. +78^F with <45%RH is comfortable, saves electricity, and minimizes the condesation of moisture in walls, ducts, and on grills.
Your oversized a/c allows using thermastat setup when the home is not occuppied. This has potiential to save a lot of energy. In addition to moisture condensation on cold surfaces, cooling with a/c removes <2 pints per KW. The high efficiency dehus like Ultra-Aires remove 5 pints per KW.
Keep your a/c and get a dehumidifier! Nobody can size an a/c to provide humidity control for the wet, cool weather. If so, get it money back in writing.

I think what he means by the fresh being introduced is keep the unit from short cycling and not having time to remove any moisture. the outside air will be humid but the larger unit will dry it out, the only thing is that the amount will need to be damper controlled and appropriate exhaust/relief measures taken to remove the conditioned air from the space. Then you are using the outside air as make-up air.

The whole house humidity control sounds like the best option for now, but if the system is that oversized, it will need to be replaced.